Tapered magnetron cathode



Dec. 13, 1955 5, WHEELER 2,727,186

TAPERED MAGNETRON CATHODE Filed Oct. 29, 1954 II T 22 2 Fig.|.

WITNESSES INVENTOR Myron S.Wheeler WMM. Z5M

ATTORNEY United States Patent TAPERED MAGNETRON CATHODE Myron S. Wheeler, Baltimore, Md., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application October 29, 1954, Serial No. 465,514

1 Claim. (Cl. 31539.75)

My invention relates to magnetrons and in particular relates to magnetrons in which cylindrical cathodes are surrounded by annular anodes which substantially close off the intervening reaction space at one end, but leave a substantially open chamber at the other end. It is found that the dissymmetry of such an arrangement results in an erosion of the electron-emissive coating of the cathode which is much more rapid at the closed end of the anode than at the other end. My invention comprises a structure which neutralizes this dissymmetry in cathode erosion and consists in using a tapered cathode, i. e., a cathode which is a truncated cone. Experimentally it has been found that tube life and efiiciency are thereby improved.

One object of my invention is accordingly to provide a new and improved type of magnetron.

Another object is to provide a novel type of cathode particularly adapted for magnetrons having reaction spaces which are closed at one end of the anode.

Another object is to provide a novel cathode for magnetrons which have axially 'dissymmetrical anode structures.

Other objects of my invention will become apparent upon reading the following description taken in connection with the drawings in which Fig. 1 is a section in a radial plane II, and Fig. 2 is a section on the plane 11-11 of Fig. 1, of a magnetron embodying the principles of my invention.

Referring to the drawings in detail a magnetron has an annular anode 1 of usual type provided with resonating cavities 2 connected with the inner face of the annulus. The anode 1 is positioned between the poles 4 and 5 of the usual magnet, but is positioned close to magnet pole 4 so that the latter virtually closes ofi the adjacent end of the annular reaction space 6, while leaving a large chamber 7 adjacent the opposite end of the anode. The cathode 8 is supported coaxial with anode 1 and is provided internally with suitable heating means (not shown) well known in the magnetron art. The active electronemissive surface of cathode 8 is a tapered, i. e., a conical, surface 9 which is coated with conventional thermionically-emissive material such as a barium oxide-strontium oxide mixture well known in the art. At opposite ends of the conical portion 9 are caps 11, 12 of well-known type. The larger-diameter end of conical surface 9 is nearer the closed end of reaction space 6 adjacent magnet pole 4. Cap 12 may, as shown, be wholly within chamber 7 beyond the face of anode 1.

The anode 1 is enclosed within a cylindrical metal Wall 13 which is connected by vacuum-tight joints with the magnets 4 and 5 and the latter are extended by metallic walls 14, 15 to glass end caps 16, 1'7 to which they are sealed to form a vacuum tight enclosure. The cathode 8 is supported on a tubular arm 18 through which in-leads to the cathode heater extend in a way well known in the magnetron art, and the other end of cathode S is supported by a quartz ring 19 which engages the magnet pole 5.

One slot 20 in anode 1 is open at its radially-outward end and provides an outlet for radiant energy into an offtake 21 to which a Waveguide or other power output channel (not shown) is connected. The lower face of the otftake 21 is provided with a slot 22 which registers with the end of slot 20.

To give a specific exemplification of a structure embodying my invention the anode 1 may have an internal diameter of .3125 in. and an external diameter of 1.410 in. and be .420 in. long between end faces. The distance between adjacent faces of magnet poles i and 5 may be .850 in. and the axial length of chamber 7 may be .450 in. The conical surface of the cathode 9 may have a maximum diameter of .230 in., a minimum diameter of .210 in. and an axial length of .370 in. The caps 11 and 12 may be .260 in. in outside diameter and .170 in. in axial length. Such a magnetron may operate with an anode voltage of 2000 and anode current of .250 amperes. The magnetic field between poles 4 and 5 has a mean strength of 5000 gausses. The resonator may be of the rising sun type having 17 identical large resonators and 17 identical small resonators. The large resonators may have an outer diameter of 1.410 in. and a slot width of .015 in. at one end to .155 at the other. The small resonators may have an outer diameter or" .7375 in. and a slot width of .015 in. at one end to .090 in. at the other.

I claim as my invention:

A magnetron comprising a substantially cylindrical envelope wall, an annular anode coaxial therewith and comprising a plurality of resonating cavities symmetrically spaced about the inner periphery of said anode, said anode being positioned closer to one end wall of said envelope than to the other, a cathode having an electronemissive conical surface coaxially positioned within said inner periphery with its larger end toward said one end wall.

No references cited. 

